Thermal cutout switches



Dec. 4, 1951 J, R -z 2,577,425

THERMAL CUTOUT SWITCHES Filed June 1, 1950 EPatesited fies. 4, 395iNITED STATES PATENT OFFICE mama CUTOUT swrrcins Jean Marcos, nun-Mums,France Application June 1, 1950, Serial No. 185,4

France July 29, 1049 2 Claims. (CL 200-118) This invention relates toautomatic cut-out switches of the kind used to protect branch circuitsagainst overload and short circuits. Such devices are particularlyuseful in cases where circuit-breakers having a high breaking capacitywould be too expensive or too spaceconsuming to be practical.

In cut-out switches of this class, the switch operates to cut thecircuit under the influence of a heat-responsive device, theelectro-magnetic means used in the larger circuit-breakers are notpracticable because they would be too complicated and expensive. As aresult, the breaking power of such small automatic cutout switches ismuch lower than that of the circuitbreakers, because the breakage periodis longer and the resulting arc is not efficiently blown out.

Another drawback of known cut-out switches of the category contemplatedby the invention is that if it is desired to prevent the possibility orforcibly maintaining the device in engaged or contact-making conditionafter it has operated due to an overload, by continued pressure on itspush-button, it is generally necessary to provide a comparativelyintricate device, sometimes known as an interlock, interposed betweenthe push-button and the movable contacts and acting to make itimpossible to prevent the device from disengaging its contact freely aslong as an overload condition persists in the rcuit. I

It is an object of this invention to provide an improved automaticcut-out switch of the class described, including a heat-responsivecontrolmeans, which is free of the above-defined inconveniences, and isparticularly simple in construction and efficient in operation.

My improved cut-out switch essentially comprises at least one pair ofmovable cooperating contacts, possessing a circuit-making position inwhich said contacts are engaged with each other, means biassing one ofsaid contacts away from and the other contact towards said position,spring-latch means adapted to releasabiy retain said one contact in itssaid position, currentresponsive means such as a bi-metal strip adaptedunder an overload to withdraw said latch to release said one contact,and a movable operating member, such as a push-button, adapted whenactuated first to positively move said one contact to its said positionagainst its related biassing means and then to positively move saidother contact slightly away from its said position against its relatedbias-sing means,

said operating member when released allowing said other contact toreturn to its contactmakin position under the action of its relatedbiassing means and being moved itself to a position clear of said onecontact.

The movable contacts are preferably carried on parallel-spaced springarms the inherent resiliency of each of which provides the saidrespective biassing means, both said arms being biassed so as to beurged in a common direction, and said other arm being positivelyarrested in said direction at its said contact-making position by astop.

The operating member is preferably a pushbutton provided with a weakspring, said button being adapted to occupy a different one of twopositions in each condition of the switch, thereby clearly showingwhether the switch is engaged or disengaged.

According to another feature, the bi-metal strip is U-shaped and thespring-arms of the contacts and the arms of the U-shaped strip are usedto form a pair of serially connected parallelly-disposed loop circuitsproviding an arc blowout circuit.

The device so constructed has a high breaking power because itscircuit-breaking action is very fast and because of the provision forblowing the arc, the arc blow-out means being obtained in a very simplemanner and without having to provide any additional parts or connectionssimply by an appropriate relative arrangement between the contacts andthe bi-metal strip. Moreover, the switch does not include an interlookwhile at the same time making it possible, as will more clearly appearhereinafter, to prevent the circuit from being broken in case of anoverload.

Furthermore, the device is comparatively very simple, being free ofpivots, pawls, levers, sliders and similar mechanical parts found inconventional units of this class, and this makes for increasedruggedness at the same time as a high degree of accuracy andpositiveness in operation, since it does not include a single mechanicalpart liable to acquire play.

The above and further objects, features and advantages of the inventionwill appear from the ensuing description made with reference to theaccompanying drawing, in which:

Fig. 1 shows one embodiment of a circuitbreaker according to theinvention, in engaged or circuit-making condition;

Fig. 2 is a cross-section of Fig. 1 on a transverse plane;

Fig. 3 is a view similar to Fig. 1 showing the device in disengaged orcircuit-breaking condition;

Fig. 4 diagrammatically illustrates the conmotions and the current paththrough the movable contacts and a bi-metal strip, providing anarc-blowout loop circuit.

As shown in the drawings my improved circult-breaker comprises a pair ofcontacts i and 2 respectively carried by spring-arms 3 and 4. To the end5 of the spring-arm 3 there is secured another and weaker spring-arm 6.The pushhutton i is formed with a shank or extension ll which bears onthe spring-arm 4. A coil spring 8 urges the push-button I to itsdepressed position. A spring-plate l0 formed with a proiecting nose 9near its top releasably engages over the spring-arm 9 and holds it downunder tension in the position shown in Fig. 1. The device includes acurrent-responsive means herein shown as a U-shaped bi-metal strip I2adapted to be distorted in the event of an overload. The strips orspring-arms 3 and 4 are connected in a circuit with the arms oi. theU-strip in the manner shown in Fig. 4, forming as shown a pair ofparallel paths for the electric current through both of which thecurrent flows in the same direction. A set screw it or the like bearingupon an insulating element I4 is interposed between the strip l0 and thebi-metal strip l2. The part l4 issupported on the strip 10.

The device operates as follows:

In the current-breaking or disengaged position of the device (Fig. 3)the spring-arms 3 and 8 press the push-button 1 outwardly against thespring-force of the coil spring 9. To coc or engage the device, thebutton I is depressed, which first applies the arm 6 against the arm I,then, as pressure continues to be applied to the button, causes bothsaid arms to be moved down bodily until the strip or arm 6 engages underthe nose 9 of the strip 10. Towards the end of this downward movement,the end of the shank ll extending the push-button engages the topsurface of the lower spring-arm 4 and depresses it by a small amount, sothat the contact between i and 2 only becomes effective after the button1 has been released and allowed to move up again slightly under theinfluence of the resiliency of the spring arm 4. If an overload occursin the circuit, the bi-metal strip i2 is distorted sufilciently todeflect the strip 10 through the medium of screw l3 and cause theprojection 9 to release the spring-arm, so that the spring assembl ofarms 3 and 6 flies upwards under their inherent resiliency more powerfulthan the force of coil spring 8, thus restoring the device to thecircuit-breaking condition of Fig. 3. The screw 13 serves as a set screwand enables adjustment of the operating point of the switch. A stop l6restricts the upward movement of the spring arm 4 and holds it at itscircuit-making position.

The circuit connections between the contacts and the bi-metal strip areso efiected, see Fig. 4, that the current will flow therethrough in thedirection indicated by the arrows in that figure; that is the currententers at a into the strip I2, flows out from the strip at b, enters thespring-arm 4 at c, passes through the contacts 4 3-1 and flows out ofthe arm 8 at d. It will be seen that the arrangement in efleetconstitutes a pair of blow-out loops in a common direction adapted toblow the are violently outwardly of the device.

when the switch is in its engaged condition and pressure is maintainedon the button E, the disengagement can be normally accomplished in caseof an overload, since. as clearly shown in Fig. 1, the base flange it ofthe push-button does not engage the surface 0! arm 9, and leaves ampleclearance for the upward disengaging movement of this spring arm whensuch movement is allowed by the withdrawal of the latching nose it awayfrom it by distortion oi the bi-metal strip.

It will be understood that many variations may be made in the details ofembodiment illustrated and described in connection with the singleillustrative embodiment shown, without exceeding the scope of theinvention.

What I claim is:

1. Circuit-breaker which comprises in combination a pair of spring-armseach carrying one of a pair of cooperating contacts, one of said armsbeing biassed away from, and the other towards, a contact-makingposition, a springstrip resiliently movable in a plane perpendicular tothe plane of movement of said arms, a nose projecting from saidspring-strip and adapted to retain said one arm in its said position, abi-metal strip adapted to be distorted under an overload, an adjustablescrew carried by said bi-metal strip and engaging said spring-strip,distortion of said bi-metal strip being adapted to axially move saidscrew to deflect said springstrip to withdraw said nose and release saidone contact, and a push-button having a base hearing on said one springarm and an extension bearing on said other spring arm, the dimensioningbeing such that depression of said button first moves said one arm toits latched contactmaking position. and then moves said other armslightly away from its said position, said button when released allowingsaid other arm to return under its inherent bias to its said position.

2. Circuit-breaker as in claim 1 wherein the spring-arm carrying saidone contact has secured to the free end thereof one end of a furtherspring-strip biassed in the same direction as said spring-arm and thebase of said push-button engages said further spring-strip.

JEAN MARCOZ.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,057,093 Geisslinger Oct. 13.1936 2,198,358 Vaughan Apr. 23, 1940 2,261,366 Grout Nov. 4, 19412,293,382 Case et al. Aug. 18, 1942 2,458,807 Tucker Jan. 11, 1949FOREIGN PATENTS Number Country Date 334,891 Germany Mar. 23. 1921370,035 Germany Feb. 26, 1923 794,535 France Dec. 12, 1935

